I believe there is a list of waypoints for the dirt pile spawns. You can download Tom Tom and Paste then use this set up to fly around looking for dirt. As for getting lovely apples specifically, I pretty sure it's random and no one place to farm for just apple spawns.

If the mounds of Dark Soil are still popping with same frequency as I remember from the pre-Dreanor days, shouldn't be too hard to get to Best Friends with Sho. Give her everything you're getting from the dirt piles. Admittedly 40% less rep from things other than the apples, but it adds up fast.

Also hit other zones besides Valley of 4 Winds. I almost always saw 2 or 3 dirt piles in Jade Temple Grounds, for example.

Have you tried the addon called Dark Soil? It's an absolute life saver, and basically shows all soil spawn points on your mini map. It works as part of TomTom but you don't have to deal with all the copy / pasting and has it own settings, etc. Helped me finish all the Tillers relationships in a few days.

I have to say thanks OP for asking this question, I was originally stuck with trying to be BFFs with Sho that I didn't know how to start. I found that if you spend about about 30 mins collecting all the dark soils around the little farming area (not the one at halfhill, but the one where Haohan Mudclaw lives, that general area) you can pick up all of what you need and more in just 2 runs.

Meaning if you spend 30 mins grabbing them all, then log and come back in a while so they respawn and pick them up all again. I did this and went from like strangers with Sho to BFFs, having the Darkmoon buff helps also. I didn't realize how easy this pet was to get! So thanks again for asking the question, and trust me its easy and sorta fun!